People use insulating material in many environments to protect themselves against heat or cold. Often, this insulating material is worn as clothing for work or recreation. For example, insulating gloves may protect a welder's hands from heat and slag. Likewise, an insulating jacket may protect a wearer from cold weather for extended outdoor recreation. Many types of insulating apparel are available, such as hats, gloves, mittens, socks, shoes, boots, pants, shirts, coats, jackets, overalls, coveralls, and the like.
Although insulating clothing may protect a wearer from extreme temperatures, some types of insulating apparel also tend to trap moisture near a wearer. Moisture from rain, snow, perspiration, or the like, is likely to accumulate in the apparel over time. In a cold environment, trapped moisture conducts heat away from the wearer, causing discomfort or pain. If heat conduction through the trapped moisture continues, a wearer may experience dangerous conditions, such as hypothermia or frostbite.
Some insulating clothing includes a waterproof, but breathable, outer layer, which prevents moisture derived from rain or snow from entering the garment, while allowing water vapor from light perspiration to escape. However, a waterproof, but breathable, outer layer naturally transmits water molecules slowly, and may still trap moisture from heavier perspiration near the wearer's skin. Thus, a person engaging in more strenuous activity, often typical of prolonged cold-weather work or recreation, may still become wet, cold, and uncomfortable.